The track, which marks the band's second Australian number one after 'We Are Young' earlier this year, knocks Pink's 'Blow Me (One Last Kiss)' down to two, while Rudimental's 'Feel The Love' completes the top three.
Meanwhile, Maroon 5's 'Feel The Love' vaults 21 to four, Owl City and Carly Rae Jepsen's 'Good Time' leaps 11 to six, and Flo Rida's 'Whistle' completes the top ten.
Further down the chart, Missy Higgins jumps 31 to 11 with 'Everyone's Waiting', B.o.B and Taylor Swift's 'Both Of Us' climbs 26 to 14, and Train bound 33 to 16 with '50 Ways To Say Goodbye'.
Florence + the Machine's 'Spectrum' debuts at 30, Pitbull and Shakira enter at 31 with 'Get It Started', and Labrinth's 'Last Time' lands at 40.
The Top 10 singles in full (click where possible for our reviews):
1. (2) fun. 'Some Nights'
2. (1) Pink: 'Blow Me (One Last Kiss)'
3. (3) Rudimental ft. John Newman: 'Feel The Love'
4. (21) Maroon 5: 'One More Night'
5. (4) Katy Perry: 'Wide Awake'
6. (11) Owl City ft. Carly Rae Jepsen: 'Good Time'
7. (5) Justice Crew: 'Boom Boom'
8. (7) will.i.am ft. Eva Simmons: 'This Is Love'
9. (8) Chris Brown: 'Don't Wake Me Up'
10.(6) Flo Rida: 'Whistle'
Watch fun.'s 'Some Nights' music video below: